A large variety of products useful, for instance, as nonionic surfactants, wetting and emulsifying agents, solvents, and chemical intermediates, are prepared by the addition reaction (alkoxylation reaction) of alkylene oxides (epoxides) with organic compounds having one or more active hydrogen atoms. For example, particular mention may be made of the alkanol ethoxylates and alkyl-substituted phenol ethoxylates prepared by the reaction of ethylene oxide with aliphatic alcohols or substituted phenols of about 6 to 30 carbon atoms. Such ethoxylates, and to a lesser extent corresponding propoxylates and compounds containing mixed oxyethylene and oxypropylene groups, are widely employed as nonionic detergent components of commercial cleaning formulations for use in industry and in the home. As another example, the addition reaction of propylene oxide with polyols provides intermediates for the preparation of polyurethane products.
An illustration of the preparation of an alkanol ethoxylate (represented by formula III below) by addition of a number (n) of ethylene oxide molecules (formula II) to a single alkanol molecule (formula I) is presented by the equation ##STR1##
The addition of alkylene oxides to alcohols and other active hydrogen containing compounds is known to be desirably promoted by a catalyst which is in conventional practice either basic or acidic in character. Recognized in the art as suitable basic catalysts are the basic compounds of the alkali metals of Group I of the Periodic Table, e.g., sodium, potassium, rubidium, and cesium, and the basic salts of certain of the alkaline earth metals of Group II of the Periodic Table, e.g., calcium, strontium, barium and in some cases magnesium. Conventional acidic alkoxylation catalysts include, broadly, Lewis acid or Friedel-Crafts catalysts. Specific examples of these acid catalysts are the fluorides, chlorides, and bromides of boron, antimony, tungsten, iron, nickel, zinc, tin, aluminum, titanium and molybdenum. The use of complexes of such halides with, for example, alcohols, ethers, carboxylic acids, and amines has also been reported. Still other examples of known acidic alkoxylation catalysts are sulfuric and phosphoric acids; perchloric acid and the perchlorates of magnesium, calcium, manganese, nickel and zinc; certain metal oxalates, sulfates, phosphates, carboxylates and acetates; alkali metal fluoroborates; zinc titanate, and certain metal salts of benzene sulfonic acid.
Other art on the subject of alkoxylation includes U.S. Pat. No. 4,727,199 which describes a process for reacting a liquid or solid alkylene oxide with a liquid or gaseous active hydrogen compound in the presence of a catalytic amount of an anion-bound metal oxide heterogenous catalyst, wherein the anion is SO.sub.4, BF.sub.4, CO.sub.3, BO.sub.3, PO.sub.4, SeO.sub.4, MoO.sub.4, B.sub.4 O.sub.7 or PF.sub.6 and the metal oxide is an oxide of zirconium, nickel, aluminum, tin, calcium, magnesium, iron, titanium, thorium, hafnium, or rubidium. Still other prior art describes the use of zeolitic materials as alkoxylation catalysts, while European patent application 0250168 and other art cited therein disclose lamellar clay catalysts.
Alkylene oxide addition reactions are known to produce a product mixture of various alkoxylate molecules having different numbers of alkylene oxide adducts (oxyalkylene adducts), e.g., having different values for the adduct number n in formula III above. The adduct number is a factor which in many respects controls the properties of the alkoxylate molecule, and efforts are made to tailor the average adduct number of a product and/or the distribution of adduct numbers within a product to the product's intended service. In certain preferred embodiments, the present invention provides a process characterized by enhanced selectivity for the preparation of alkoxylate mixtures in which a relatively large proportion of the alkoxylate molecules have a number (n) of alkylene oxide adducts that is within a relatively narrow range of values.
It is known in the art that alcohol alkoxylate products having a narrow range alkylene oxide adduct distribution are preferred for use in certain detergent formulations (Great Britain Patent No. 1,462,134, Derwent Publications Research Disclosure number 194,010). Narrow-range alcohol alkoxylates are also known to be particularly valuable as chemical intermediates in the synthesis of certain carboxyalkylated alkyl polyethers (U.S. Pat. No. 4,098,818) and of certain alkyl ether sulfates (Great Britain Patent No. 1,553,561). Conventional commercial alkoxylate preparation, which has in large part been limited to the use of basic catalysts. particularly the metals sodium and potassium and their oxides and hydroxides, yields only a relatively broad distribution range product. Conventional acid-catalyzed alkoxylation reactions have long been known to produce a more narrow range product than that obtained with the alkali metal catalysts. However, acid catalysts have substantial disadvantages in several other respects. For instance, the acids are often unstable with limited life and effectiveness as catalysts in the alkoxylation mixture. Both the acid catalysts themselves and their decomposition products catalyze side reactions producing relatively large amounts of polyalkylene glycols, and also react directly with the components of the alkoxylation mixture to yield undesirable, and often unacceptable, by-products such as organic derivatives of the acids.
Also of substantial importance in alkoxylation processes is the ability of the process to minimize the quantity of unreacted (or residual) active hydrogen reactant remaining in the final product. A high level of residual reactant either represents a loss of valuable reactant, or requires that further processing of the product be carried out to recover the reactant. Moreover, the presence of the unreacted material is often a disadvantage from the standpoint of product quality and environmental concerns. For instance, residual alkanol in a detergent alcohol ethoxylate product contributes to volatile organic emissions during spray drying of detergent formulations.
It has recently been reported in the art that, in addition to conventional acidic catalysts, a number of other substances have been found to function as catalysts or in co-catalyst combinations which are capable of producing relatively narrow distributions for the oxyalkylene adducts of higher alkanols and other active hydrogen containing compounds. For instance, it has recently been disclosed (U.S. Pat. Nos. 4,306,093 and and 4,239,917, and published European Patent Application Nos. 0026544, 0026546, 0026547) that certain compounds of barium, strontium, and calcium promote narrow-range alkoxylation products. U.S. Pat. Nos. 4,210,764 and 4,223,164 describe the use of cresylic acids to promote alkoxylation catalyzed by barium and strontium compounds. U.S. Pat. No. 4,302,613 discloses that a more peaked reaction product can be obtained by combining barium and strontium alkoxylation catalysts with co-catalysts such as calcium oxide, calcium carbide, calcium hydroxide, magnesium metal, magnesium hydroxide, zinc oxide and aluminum metal. U.S. Pat. No. 4,453,023 describes a process for preparing alkoxylates having a narrower molecular weight distribution which employs a catalyst comprising a barium compound and a promoter selected from the class consisting of superphosphoric acid, phosphoric acid, diphosphoric acid, triphosphoric acid, phosphorous acid, dihydrogen phosphate compounds, oxides of phosphorus, carbon dioxide, and oxalic acid. U.S. Pat. No. 4,453,022 describes a similar process wherein the catalyst comprises a calcium or strontium compound and a promoter selected from the class consisting of superphosphoric acid, phosphoric acid, diphosphoric acid, triphosphoric acid, phosphorous acid. dihydrogen phosphate compounds, oxides of phosphorus, sulfuric acid, bisulfate compounds, carbonic acid, bicarbonate compounds, carbon dioxide, oxalic acid and oxalic acid salts, sulfur trioxide, sulfur dioxide, and sulfurous acid. Published PCT application WO 85/00365 discloses other activated calcium containing alkoxylation catalysts capable of producing narrow range alkoxylation products. U.S. Pat. No. 4,375,564 reports that a narrow range product results from alkoxylation reactions catalyzed by a magnesium compound in combination with a compound of one of the elements aluminum, boron, zinc, titanium, silicon, molybdenum, vanadium, gallium, germanium, yttrium, zirconium, niobium, cadmium, indium, tin, antimony, tungsten, hafnium, tantalum, thallium, lead and bismuth. U.S. Pat. No. 4,483,941 discloses catalysts for alkoxylation reactions which comprise either BF.sub.3 or SiF.sub.4 in combination with an alkyl or alkoxide compound of aluminum, gallium, indium, thallium, titanium, zirconium, and hafnium. U.S. Pat. No. 4,456,697 describes an alkoxylation catalyst which comprises a mixture of HF and one or more metal alkoxides. Japanese patent specification 52051307 to Tokuyama Soda KK discloses the selective preparation of mono- rather than di- or tri-alkylene glycol esters from alkylene oxide and alcohol using solid acid catalysts such as silica, alumina, titania, vanadium pentoxide, antimony pentoxide, titanyl sulfate, tungstic acid, phosphotungstic acid, and silver perchlorite.
Recently issued U.S. Pat. No. 4,721,816 claims a process for preparing narrow range distribution alkoxylates, wherein the catalyst is a combination of one or more sulfur-containing acids with one or more aluminum alcoholate or phenolate compounds. U.S. Pat. No. 4,721,817 claims a similar process wherein the combination contains one or more phosphorus-containing acids.
U.S. Pat. Nos. 4,665,236 and 4,689,435 describe a process for the alkoxylation of active hydrogen reactants using certain bimetallic oxo catalysts. The catalysts described in U.S. Pat. No. 4,665,236 include compounds in which one of the metal species in the bimetallic molecule is lanthanum, and European application 0250168 discloses lamellar clay catalysts which have been ion exchanged with lanthanum and other rare earth elements.
The alkoxylation catalysts in the references discussed above are prepared by conventional methods such as simple chemical reactions, i.e., acid-base or metathesis reactions, or methods known in the art such as ion exchange.
It has now been found that hydrogel-derived xerogels comprising one or more compounds comprising a rare earth element and phosphorus are effective catalysts for the addition reaction of alkylene oxides with organic compounds having active hydrogen atoms. It has further been found that, in certain preferred embodiments, an alkoxylation reaction catalyzed by a xerogel comprising one or more compounds comprising a rare earth element and phosphorus provides an alkoxylate product, particularly an alkanol ethoxylate product, of exceptionally narrow-range alkylene oxide adduct distribution.